We present preparation and spectroscopic characterization of the Tm-doped fibers with enhanced 3H4 fluorescence lifetime thanks to codoping with alumina. With the alumina content of 10 mol %, the fluorescence lifetime of 58 μs was achieved. Using experimentally obtained fiber characteristics, we used numerical simulations to study and optimize for the first time the thulium-doped fiber amplifier (TDFA) with dual wavelength (800 + 1400 nm) pumping scheme where the pump at 800 nm propagates in the cladding and the other pump propagates in the core. The results are compared with numerical simulations of TDFA pumped at single-wavelength in the 1050 nm band.